Reflex: Difference between revisions

Naively, we might imagine that reflexes are immutable. In reality, however, most reflexes are flexible and can be substantially modified to match the requirements of the behavior in both vertebrates and invertebrates.<ref>{{cite journal | vauthors = Pearson KG | title = Common principles of motor control in vertebrates and invertebrates | journal = Annual Review of Neuroscience | volume = 16 | pages = 265–97 | date = 1993 | pmid = 8460894 | doi = 10.1146/annurev.ne.16.030193.001405 }}</ref><ref>{{cite journal | vauthors = Büschges A, Manira AE | title = Sensory pathways and their modulation in the control of locomotion | journal = Current Opinion in Neurobiology | volume = 8 | issue = 6 | pages = 733–9 | date = December 1998 | pmid = 9914236 | doi = 10.1016/S0959-4388(98)80115-3 | s2cid = 18521928 }}</ref><ref>{{cite journal | vauthors = Tuthill JC, Azim E | title = Proprioception | language = English | journal = Current Biology | volume = 28 | issue = 5 | pages = R194-R203R194–R203 | date = March 2018 | pmid = 29510103 | doi = 10.1016/j.cub.2018.01.064 | doi-access = free }}</ref>

A good example of reflex modulation is the [[stretch reflex]].<ref>{{Cite journal| vauthors = Bässler U |date=1976-03-01|title=Reversal of a reflex to a single motoneuron in the stick insect Çarausius morosus |journal=Biological Cybernetics|language=en|volume=24|issue=1|pages=47–49|doi=10.1007/BF00365594|s2cid=12007820|issn=1432-0770}}</ref><ref>{{cite journal | vauthors = Forssberg H, Grillner S, Rossignol S | title = Phasic gain control of reflexes from the dorsum of the paw during spinal locomotion | journal = Brain Research | volume = 132 | issue = 1 | pages = 121–39 | date = August 1977 | pmid = 890471 | doi = 10.1016/0006-8993(77)90710-7 | s2cid = 32578292 }}</ref><ref>{{cite journal | vauthors = Capaday C, Stein RB | title = Amplitude modulation of the soleus H-reflex in the human during walking and standing | journal = The Journal of Neuroscience | volume = 6 | issue = 5 | pages = 1308–13 | date = May 1986 | doi = 10.1523/JNEUROSCI.06-05-01308.1986 | pmid = 3711981 | pmc = 6568550 }}</ref><ref name=":0">{{cite journal | vauthors = Clarac F, Cattaert D, Le Ray D | title = Central control components of a 'simple' stretch reflex | journal = Trends in Neurosciences | volume = 23 | issue = 5 | pages = 199–208 | date = May 2000 | pmid = 10782125 | doi = 10.1016/s0166-2236(99)01535-0 | s2cid = 10113723 | url = https://hal.archives-ouvertes.fr/hal-02346762/file/2000%20Clarac%20et%20al%20-%20TrendsNeurosci.pdf }}</ref> When a muscle is stretched at rest, the stretch reflex leads to contraction of the muscle, thereby opposing stretch (resistance reflex). This helps to stabilize posture. During voluntary movements, however, the intensity (gain) of the reflex is reduced or its sign is even reversed. This prevents resistance reflexes from impeding movements.

The underlying sites and mechanisms of reflex modulation are not fully understood. There is evidence that the output of sensory neurons is directly modulated during behavior—for example, through [[presynaptic inhibition]].<ref>{{cite journal | vauthors = Wolf H, Burrows M | title = Proprioceptive sensory neurons of a locust leg receive rhythmic presynpatic inhibition during walking | journal = The Journal of Neuroscience | volume = 15 | issue = 8 | pages = 5623–36 | date = August 1995 | doi = 10.1523/JNEUROSCI.15-08-05623.1995 | pmid = 7643206 | pmc = 6577635 }}</ref><ref>{{cite journal | vauthors = Sauer AE, Büschges A, Stein W | title = Role of presynaptic inputs to proprioceptive afferents in tuning sensorimotor pathways of an insect joint control network | journal = Journal of Neurobiology | volume = 32 | issue = 4 | pages = 359–76 | date = April 1997 | pmid = 9087889 | doi = 10.1002/(SICI)1097-4695(199704)32:434<359::AID-NEU1>3.0.CO;2-5 }}</ref> The effect of sensory input upon motor neurons is also influenced by interneurons in the [[spinal cord]] or [[ventral nerve cord]]<ref name=":0" /> and by descending signals from the brain.<ref>{{cite journal | vauthors = Mu L, Ritzmann RE | title = Interaction between descending input and thoracic reflexes for joint coordination in cockroach: I. descending influence on thoracic sensory reflexes | journal = Journal of Comparative Physiology A: Neuroethology, Sensory, Neural & Behavioral Physiology | volume = 194 | issue = 3 | pages = 283–98 | date = March 2008 | pmid = 18094976 | doi = 10.1007/s00359-007-0307-x | s2cid = 25167774 }}</ref><ref>{{cite journal | vauthors = Martin JP, Guo P, Mu L, Harley CM, Ritzmann RE | title = Central-complex control of movement in the freely walking cockroach | journal = Current Biology | volume = 25 | issue = 21 | pages = 2795–2803 | date = November 2015 | pmid = 26592340 | doi = 10.1016/j.cub.2015.09.044 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Hsu LJ, Zelenin PV, Orlovsky GN, Deliagina TG | title = Supraspinal control of spinal reflex responses to body bending during different behaviours in lampreys | journal = The Journal of Physiology | volume = 595 | issue = 3 | pages = 883–900 | date = February 2017 | pmid = 27589479 | pmc = 5285725 | doi = 10.1113/JP272714 }}</ref>